Cassette type audio devices are widely used as car stereos and so forth. A prior art door mechanism of a cassette insertion opening in such an audio device has a single dust door pivotally supported at the opening. Such a dust door is made from a plastic resin, aluminum or other metals and shuts the cassette insertion opening when a cassette is not inserted therethrough to keep the interior of the audio device away from dust. When a cassette is inserted into the audio device, the dust door pivots a little inward into the audio device and remains there while the tape is driven.
Such cassette type audio devices are also used in ships and boats. Particularly, they are today in a considerable demand for small size leisure boats.
The prior art door mechanism, however, seals the audio device merely when a cassette is not inserted and remains halfway opened when the cassette is inserted. Therefore, the door cannot fully protect the interior of the audio device against water, salt and so forth and is not suitable for use in ships and boats.